On-chip reset circuitry and method

Abstract

An integrated circuit includes an external reset input, a clock input for receiving a clock signal and a reset signal sub-circuit including an internal reset output connected to other circuits of the integrated circuit. The reset signal sub-circuit immediately supplies an internal reset signal upon receipt of the external reset signal and ceases to supply the internal reset signal upon a next clock signal following ceasing to receive the external reset signal. This asynchronously forces combinational logic to a reset state upon receipt of the internal reset signal and synchronously forces sequential logic to a reset state upon receipt of a next clock signal.

1. An integrated circuit comprising:
 an external reset input for receiving an external reset signal; 
 a clock input for receiving a clock signal; 
 a reset signal sub-circuit connected to said external reset input and said clock input and including an internal reset output connected to other circuits of said integrated circuit, said reset signal sub-circuit immediately supplying an internal reset signal on said internal reset output to reset said other circuits upon receipt of said external reset signal and ceasing to supply said internal reset signal on said internal reset output upon a next clock signal received at said clock input following ceasing to receive said external reset signal at said external reset input; and 
 said other circuits includes a combinational logic circuit including an AND gate having at least one input receiving a corresponding data signal and a further input receiving said internal reset signal. 
 
   
   
     2. The integrated circuit of  claim 1  wherein:
 said reset signal sub-circuit includes a flip flop having an asynchronous reset input connected to said external reset input, a clock input connected to said clock input, a data input connected to said external reset input, and a data output connected to said internal reset output. 
 
   
   
     3. The integrated circuit of  claim 1  wherein:
 said other circuits includes a register having a plurality of bit circuits, each bit circuit having
 a flip flop with a clock input receiving said clock signal, a data input and a data output, and 
 an AND gate having a first input receiving a bit input for said bit circuit, a second input receiving said internal reset signal and an output connected to said data input of said flip flop. 
 
 
   
   
     4. An integrated circuit comprising:
 an external reset input for receiving an external reset signal; 
 a clock input for receiving a clock signal; 
 a reset signal sub-circuit connected to said external reset input and said clock input and including an internal reset output connected to other circuits of said integrated circuit, said reset signal sub-circuit immediately supplying an internal reset signal on said internal reset output to reset said other circuits upon receipt of said external reset signal and ceasing to supply said internal reset signal on said internal reset output upon a next clock signal received at said clock input following ceasing to receive said external reset signal at said external reset input; and 
 said other circuits includes a register having a plurality of bit circuits, each bit circuit having
 a flip flop with a clock input receiving said clock signal, a data input and a data output, and 
 an AND gate having a first input receiving a bit input for said bit circuit, a second input receiving said internal reset signal and an output connected to said data input of said flip flop. 
 
 
   
   
     5. The integrated circuit of  claim 4  wherein:
 said reset signal sub-circuit includes a flip flop having an asynchronous reset input connected to said external reset input, a clock input connected to said clock input, a data input connected to said external reset input, and a data output connected to said internal reset output.